Water heater control system



Patented Oct. 16, 1945 WATER HEATER CONTROL SYSTEM Clark M. Osterheld,Stoughton, Wis., asslgnor to McGraw Electric Company, Elgin, Ill., acorporation of Delaware Application July 17, 1944, Serial No. 545,354

3 Claims. (01. 219-39) My invention relates to electric heating, andparticularly to systems for controlling the energization of an electricheater for a domestic hot water tank.

Among the objects of my invention are: to pro vide a control system forthe electric heater of a domestic hot water storage tank that shallcause immediate energization of the heater in case a relatively largequantity of hot water has been withdrawn from the tank and to causedeenergization of the heater when substantially onehalf of the tank isfull of hot water; to cause energization of the heater with apredetermined time delay period after closure of a time-controlledswitch in case the tank contains only a relatively small amount of coldwater and to cause deenergization of said heater when substantially allof the water in the tank is hot, independent of the position of atime-controlled switch.

In the drawing,

Figure 1 is a view in vertical section through a usual domestic hotwater tank, with which is associated the system embodying my invention,and,

Fig. 2 is a diagram of connections embodying my invention.

Referring first to Fig. 1 of the drawing, I have there shown a domestichot water tank I I, having a lower cold water inlet pipe I3, an upperhot water outlet pipe I5, surrounded by a mass ll of heat-insulatingmaterial, which is held in place by an outer casing I9. I provide alsoan electric heater 2|, which, if only a single electric heater isprovided, is located adjacent to the lower end portion of the tank andmay be of a clamp-on typ located in a tunnel 23. While I have illutrated a specific embodiment of a domestic hot water tank and of anelectric heater, I do not desire to be limited thereto, since anyequivalent or similar element may be used in place thereof.

I provide a lower thermally-actuable heater control switch, designatedby numeral 25, which is positioned adjacent to the lower end of the tankThe switch 25 comprises a tube 21, having a closed inner end and havingits open outer end secured in a fluid-tight manner in an opening in tankadjacent the lower end thereof. An expansion rod 29 is positioned in thetube 21 and is adapted to engage with and be disengaged from a small lug3| of electric-insulating material secured to the free end of aresilient contact arm 33, which latter is adapted to engage with and bedisengaged from a substantially rigid contact arm 35. The two contactarms 33 and 35 may be supported by blocks 31 of electric-insulatingmaterial. The design, construction, and adjustment of the switch 25 issuch that when tube 21 is subject to cold water'in the tank, the lengthof expansion rod 29 will be such that the contact arm 33 will be inengagement with contact arm 35, while if tube 21 is subject to hotwater, the length of expansion rod 29 will be such that contact arm 33will be out of engagement with contact arm 35. When I speak of coldwater, I refer to water, the temperature of which is on the order of 60to 70 F., while when I speak of hot water, I refer towater, thetemperature of which is on the order of 150 F. or even slightly higher.

I provide a thermal retarder switch, designated generally by numeral 39,which is a modification, as will be hereinafter explained, of the devicedisclosed and claimed in my co-pending application, S. N. 537,941, filedMay 29, 1944, and assigned to the same assignee as is the presentapplication.

The thermal retarder heater control switch unit 39 comprises a firstthermal switch having a first bimetal bar 4| and a second bimetalbar-43. The two bimetal bars 4| and 43 are adapted to be positioned inabutting engagement relatively to each other, the bimetal bar 4| beingprovided with a plurality of pivot plates 45 secured to its outer end,while the bar 43 is provided with sharpened ends adapted to pivotallyengage the pivot plates 45. The two bars 4| and 43 are each providedwith a central longitudinally-extending slot in the adjacent abuttingend portions, and an over center spring 41 is positioned in the slots,the ends of spring 41 being secured to the bars 4| and 43 adjacent theends of the respective slots, so that the free end of bimetal bar 43will move with a snap action upon change of temperature.

I provide a contact bridging member 49 insulatedly mounted on the outerend of bimetal bar 43, which is adapted to engage with and be disengagedfrom a pair of fixed contact members 5| and 53. When the bimetal bar 4|is subject to cold water in the tank, the position of the bimetal bars4| and 43 will be that shown in Fi 2 of the drawing, and contactbridging member 49 will be in contacting engagement with the contacts 5|and 53. When the first thermal switch is subject to hot water in thetank, the bimetal bars 4| and 43 will have moved into the oppositeposition, where bimetal bar 43 will be in engagement with a stop member55, such movements occurring with a snap action.

I provide a second snap-acting thermal switch in the thermal retarder39, comprising a first blmetal bar 51, a second bimetal bar 59,positioned in pivotally abutting end-to-end relation, sharpened endportions at the inner end of bimetal bar 59 engaging pivot plates 6| onthe outer end of bimetal bar 51. An over center spring 63 is positionedin two aligned slots provided in the two bimetal bars 51 and 59, theends of spring 53 being secured to the intermediate portions of thebimetal bars 51 and 59. I provide a contact bridging member 55insulatedly mounted on the outer free end of bimetal bar 59, and thedesign and-construction of the second thermal switch is such' thatcontact bridging member 65 will be out of engagement with two fixedcontact members 61 and I59 when the thermal retarder is subject to coldwater and-also subject to hot water in the tank, but will be"in suchposition that the contact bridging member 65will be in engagement withthe contacts 61 and 69 when the bimetal bars have been heated to anappreciably higher temperature on the order of 200 to 250 F. To obtainthis increased temperature, I provide a heating coil 1| on bimetal bar51, the

energy translatable into heat in heating coil 1| being only very smalland requiring some four to six hours to cause temperature rise ofbimetal bar 51 to a temperature on the order of 200 to 250 F.

I provide a third thermal switch in the thermal retarder switch unit 39,which third switch is not disclosed in the hereinbefore mentionedco-pending application but is substantially the same as is the secondthermal switch. The third thermal switch comprises a first bimetal bar13, a second bimetal bar 15 held in abutting end-to-end relation by anover center spring 11. The sharpened inner ends of bimetal bar 15 areadapted to fit into pivot plates 19 on the outer end of bimetal bar 13,the two bars 13 and 15 being provided with aligned centrallongitudinally-extending slots, within which spring 11 is located. Acontact bridging member 8| is insulatedly positioned on the outer end ofbimetal bar 15, and as long as the temperature of bimetal bar 13 is notto exceed 150 F., bimetal bar 15 will be in engagement with a stopmember 83. However, when the temperature of bimetal bar 13 has beenraised to a value on the order of 200 to 250 F. or thereabouts, thecontact bridging member 8| will be moved into engagement with a, snapaction with a pair of fixed contacts 85 and 81. I provide also a heatingcoil 89 for the bimetal bar 13, and this heating coil is so designed andconstructed as to be traversed by the current traversing the electricheater 2 I. ,The amount of energy translated into heat in heating coil89 is relatively very small but is of such value as to cause atemperature rise in bimetal bar 13' to a value on the order of 250 F.within say fifteen to thirty minutes.

I provide further a time-controlled .switch, shown generally only inFig. 2 of the drawing as comprising a first contact arm 9| and a. secondcontact arm 93, which are adapted to be out of engagement with eachother during on-peak periods of a twenty-four hour day, but are adaptedto be in engagement with each other during oii peak periods. The designand construction of the rest of the timer mechanism is not shown, sinceI may use any one of the several devices of this general kind now on themarket.-

I provide a, first-supply circuit conductorl95 35 of the lowerthermally-actuable switch 25. Contact arm 33 is connected by a conductorI to the second supply circuit conductor 91.

A conductor I91 connects contact 53 to one terminal of heating coil 89on the bimetal bar 13 of the third thermal switch of the thermalretarder switch unit. The other terminal of heating coil 89 is connectedto a conductor I99, which connects contacts 81 and 69. Contact 61 isconnected by a conductor III with the second contact arm 93 of thetime-controlled switch. Another conductor I |3 connects contact 61 toone terminal of heating coil 1|, the other terminal of which isconnected by a conductor II5 with contact arm 35 of the switch 25.

In the usual domestic hot water tank installation, pressure is on thewater in the tank at all times, and upon withdrawal of hot water fromthe tank through the upper hot water outlet pipe I 5, a correspondingamount of cold water will enter the tank through the lower cold waterinlet pipe I 3, the cold water remaining in the lower part ofthe tankand the hot water remaining in the upper part of the tank.

Let it now be assumed that a relatively large quantity of hot water hasbeen withdrawn from the tank during on-peak hours of the day, usuallythe daylight hours, so that the thermal retarder unit 39 is subject tocold water, which will cause a snap-acting movement of the first thermalswitch of the thermal retarder, comprising bimetal bars 4| and 43, intothe position shown in full lines in Fig. 2 of the drawing, therebyclosing an energizing circuit for the heater 2|,

traceable as follows: from supply circuit conductor 95 through conductor99, through the engaged contact bridging member 49 and contacts 5| and53, through conductor |9|, heater 2|, conductor I93, through the engagedcontact arms 35 and 33, and through conductor I95 to the second supplycircui-t conductor 91.

As soon as enough water has been heated in the tank to cause the hotwater to fall below the thermal retarder 39, which may, for illustrativepurposes, be said to be positioned at substantially half of the heightof the tank, the first thermal switch of the thermal retarder unit willbe subject to hot water, with the result that the contact bridgingmember 49 will be moved out of engagement with the contacts 5| and 53with a snap action, whereby deenergization of the heater 2| is effected.It is therefore evident that in case of use of a relatively largequantity of hot water, the control system disclosed herein and discussedthus far is efiectlve to cause heating o1 enough water to fill one-halfof the tank, that is the upper half, with hot water, whereby arelatively large amount of hot water is available for ordinary householduses, irrespective of the position of the time-controlled switch.

Let it now be assumed that only a relatively small amount of hot waterhas been withdrawn from the tank during on-peak hours, so that only thelower thermally-actuable switch 25 is subject to cold water, while thethermal retarder switch unit is still subject to hot water. The heater2| will not be energized and no circuit of my improved control systemwill be closed and energized until closure of the time-controlled switchat the start of an off-peak period. This starting time may be 10 p. m.or 11 p. 111. When the two contact arms 9| and 93 are engaged, anenergization circuit is closed through heating coil 1|, traceable asfollows: from the first supply circuit conductor 95 through the engagedcontact arms 9| and 93, through conductors III and H3 to heating coilll, conductor II5, through engaged contact arms 35 and 33, and fromthere through conductor I to the second supply circuit conductor 91-. Ifit be assumed that the timecontrolled switch was closed at say o'clock,and if it be further assumed that the length of ,time necessary for coil'II cause temperature ductor I09, heating coil 89 of the third thermalswitch, through conductors I01 and IOI, heater 2 I, conductor I03,through engaged contact arms 35 and 33, and through conductor I05 to thesecond supply circuit conductor 91. As has hereinbefore been stated, thelength of time necessary -for the energized heating coil 09 to causetemperature rise of bimetal bar I3 to a value sufficient to causeclosing movement of contact bridging member BI is on the order offifteenminutes to thirty minutes, so that this action will occur after saidpredetermined relatively short delay period. This will close a newcircuit through the heating coil 2|, traceable as follows: from supplycircuit conductor 95 through conductor 99, engaged contacts 85 and 81with contact bridging member 8|, through conductor I09, heating coil 89,through conductors I01 and NI, through heater 2|, conductor I03, engagedcontact arms 35 and 33, and from there through conductor I05 to thesecond supply circuit conductor 91, This latter circuit is independentof the time-controlled clock, so that should it happen that a relativelylarge quantity of hot water is withdrawn from the tank during the verylate night hours, energization of the heater 2| will be continued, eventhe time-controlled switch, including the arms 9| and 93, is opened. Thelower thermally-actuable switch 25 will ultimately be subject to hotwater in the tank, and it will then move into open orheater-deenergizingposition, which will cause return of the variousparts of the system to their normal imoperative positions, where thefirst thermal switch will be open, as will also the second and thirdthermal switches, as well as the lower thermally-actuable switch.

The system embodying my invention is thus effective to cause maintenanceof at least onehalf tankful of hot water in the tank during onpeakperiods of a twentyfour hour day and is further efiective to ensure thatthe heater 2| will not be deenergizecl during the early morning hoursuntil substantially all of the water in the tank is hot.

Various modifications may be made in the system embodying my inventionwithout departing from the spirit and scope thereof, and all suchmodifications coming clearly within the scope of the appended claimsshall be considered as covered thereby.

I claim as my invention:

1. A control system for a domestic hot water 'tank having an electricheater, subject to withdrawals of hot water throughout a twenty-fourhour day, comprising a lower thermally-actuable heater control switchmounted inheat-recelving relation on the tank adjacent the lower endthereof, a, time-controlled switch adapted to be in closed positionduring off-peak periods only, a thermal retarder unit mounted inheat-receiving relation on the tank intermediate the ends thereof,comprising a first thermal switch adapted to be in closed position whensubject to cold water in the tank and in open position when subject tohot water in the tank, a second thermal switch adapted to be in openposition when subject to cold and to hot water in the tank and to be inclosed position when its temperature has been raised to a predeterminedappreciably higher value, a heating coil for said second switch forraising its temperature to said predetermined higher value, theenergization of said coil being controlled jointly by saidtime-controlled switch and said lower thermally-actuable switch, a thirdthermal switch adapted to be in open position when subject to cold andto hot water in the tank and adapted to be in closed position whenheated to a predetermined appreciably higher temperature and otherelectric connections between said heater and said switches to causeselective energization of said heater immediately when said thermalretarder is subject to cold water, irrespective of the position of saidtime-controlled switch, said energization continuing until the thermalretarder is subject to hot water and with a predetermined time period ofdelay after closure of said time-controlled switch in case said lowerthermally-actuable switch only is subject to cold water, saidenergization continuing until substantially all of the water in the tankis hot, irrespective of the position of the time-controlled switch.

2. A control system for a domestic hot water tank havin an electricheater, subject to withdrawals of hot water throughout a twenty-fourhour day, compising a lower thermally-actuable heater control switchmounted in heat-receiving relation on the tank adjacent the lower endthereof, a time-controlled switch adapted to be in closed positionduring oil-peak periods only, a thermal retarder unit mounted inheat-receiving relation on the tank intermediate the ends thereof,comprising a first thermal switch adapted to be in closed position whensubject to cold water in the tank and in open position when subject tohot water in the tank, a second thermal switch adapted to be in openposition when subject to cold and to hot water in the tank and to be inclosed position when its temperature has been raised to a predeterminedappreciably higher value, a heating coil for said second switch forraising its temperature to said predetermined higher value, theenergization of said coil being controlled jointly by saidtime-controlled switch and said lower thermally-actuable switch, a thirdthermal switch adapted to be in open position when subject to cold andto hot water in the tank and adapted to be in closed position whenheated to a predetermined appreciably higher temperature and otherelectric connections between said heater and said switches to causeselective energization of said heater through said lowerthermally-actuable switch and said first thermal switch as soon as saidfirst thermal switch is subject to cold water, irrespective of theposition of said time-controlled switch, said energization continuinguntil the first thermal switch is subject to hot water and with apredetermined time delay period after closure of said time-controlledswitch in case said lower thermally-actuable switch only is subject tocold water at that time, said energization being initially efiectedthrough said lower thermally-actuable switch, the heating coil of saidthird switch, said second thermal switch and said time-controlled switchand then continued through said lower thermally-actuable respective ofthe position, of the time-controlled switch.

3 A control system as set forth in claim 2,'in which deenergization ofthe heater is effected by switch, the heating coil of said third thermala said lower thermally-actuable switc when 11-, is

switch and said third thermal switch until substantially all of thewater in the tank is hot, ir-

subject to hot water.

CLARK M. OS'IERI IELD.

